Patients with diabetes mellitus who undergo percutaneous coronary intervention (PCI) have higher rates of restenosis and a poorer prognosis than patients without diabetes. The American College of Cardiology/American Heart Association guidelines on exercise testing suggest that patients with diabetes may benefit from routine post-PCI functional testing (FT). To explore this issue, we examined the functional capacity, quality of life, event rates and procedural outcomes among 61 patients with diabetes enrolled in the Aggressive Diagnosis of Restenosis (ADORE) trial. All patients were randomized to either routine FT or selective FT and were followed for a period of 9 months. Patients with diabetes randomized to routine FT had a higher composite clinical event rate than those randomized to the selective FT strategy. Procedural rates did not differ significantly between the two groups. These results suggest that routine post-PCI FT in patients with diabetes is of little clinical value.